Free machining structural alloy



Patented July '30, 1935 UNITED STATES PATENT OFFICE MACHINING STRUCTURAL ALLOY Frank R. Palmer, Reading, Pa.. assignor to The Carpenter Steel Company, Reading, Pa., a corporation of New Jersey No Drawing. Original application January .14,

1932, Serial No. 586,697.

Divided and this application May 31, 1934, Serial No. 728,306

11 Claims.

cation Ser. No. 586,697 filed January 14, 1932; the

present improvement forming a division of the aforesaid application, and relating particularly to 10 the so-called structural alloy class described therein.

In said original application I pointed out that the ferrous alloys referred to might conveniently be dividedinto four general classes designated as straight carbon steels, structural alloy steels, "tool steels and special alloy steels as fully described therein. The present invention relates to the second of the before mentioned groups namely, structural alloys, which may be defined as ferrous alloys containing less than .50% carbon, between 90% and 98% iron, with the balance non-ferrous elements ordinarily used in structuralalloy steels.

Though such structural alloy steels find their principal use as heat treated parts in the construction of automobiles, machine tools, aircraft, ordnance, and many other machines and appliances, it is commonly known that some of these compositions are used for other than structural purposes, and my use of the term structural alloy is not intended to limit the scope of my invention in terms of use or application of the finished parts. Within the chemical boundaries adopted for this particular group, my invention provides free machining and non-galling properties, the novelty and value of which is independent of the ultimate use of the finished article.

In avoiding a low limit for carbon, I do so in conformity to the standard'specifications for such structural alloy steels as S. A. E. 2512 and S. A. E. 3312 in which the carbon is specified .17% max. The lower carbon types are frequently case hardened, and the higher carbon types are usually, though not necessarily, heat treated to utilize the alloy content to best advantage.

There are an almost limitless number of alloy steels within the scope of my structural alloy group but I find it convenient to assemble them into three principal sub-groups'namely, the nickel group, the chromium group and the manganese group. The nickel group contains nickel between 1% and 6%, either alone or accompanied by other alloying elements. A few representative nickel steels are:

b A general! Car on s esire Nickel 1.25 to 1.75.

- Carbon .17 maximum. 13-2512 Nickel 415015.25.

I Carbon As desired. S. A. E. 3200 Nickel 1.50 to 2.00.

Chromium .90 to 1.25.

Carbon .15. S. A. E. 4615 Nickel 1.50 to 2.00.

' Molybdenum..... .20 to .30.

The above examples are illustrative only as nickel structural alloy steels can be compounded in many ways and even containing aluminum for nitriding purposes so that my nickel group may be defined as alloys containing less than .50% carbon, 1% to 6% nickel, with or without alloys of the group manganese-silicon-phosphorus-chromium-tungsten-vanadium aluminum molybdenum, etc. which last named group may total from 25% to 5.00%.

Structural alloy steels of, the chromium sub-group may contain 25% to 4.00% chromium,

with or without other alloying elements. For example err es re .60 to 1.10.

Carbon As desired. S. A. E. 4100 {Chromium .80 to 1.10.

Molybdenum .15 to .25.

Carbon--. As desired. S. A. E. 6100 .80 to 1.10.

- Vanadium .18.

Carbon"; As desired. 8. A. E. 7200 Chromium .50 to 1.00.

Tungstem, 1 50 to 2.00

Carbon As desired Valve steel(U. S. Pet. 1,707,364) Chromium 3.00. Silicon 2.00.

Carbon As desired. Nitriding steel Chromium 1.50.

Aluminum .75.

Thus the chromium sub-group may be modified in many ways within this definition: Carbon less than .50%, chromium 25% to 4.00%, alloys of the group manganese-silicon-phos- .phorus nickel tungsten vanadium-aluminummolybdenum totalling between 25% and 5%.

Manganese is of course present in practically tween 50% and 3.00%, as an alloy to afiect the properties of the steel, for example Manganese in excess of 50% may be added to any alloy steel to secure deeper and more rapid hardening so that such steels may be defined: Carbon less than 50%, manganese 50% to 3.00%, alloys of the group silicon-phosphoruschromiumnickel-aluminurn-vanadian molybdenum-tungsten totalling between 25% and 3.00%.

The three sub-groups set forth do not necessarily comprehend all of the compositions that fall within my broad structural alloy group and they have been so classified not to limit the scope of my invention but to clarify its presentation.

All of these structural alloy compositions can, if desired, be annealed softer than 250 Brinell hardness to render them commercially machinable, although it is .not uncommon for them to be purchased from the steel maker already heat treated to some higher physical test. Although they are inherently machinable in such condition, it is very desirable that the machinability be improved if possible-and without too much detriment tothe ultimate use of the alloys. Sulphur which has heretofore been largely used as a free machining element in carbon steels is abhorrent in alloy steels because of the large quantity of non-metallic inclusions that result from its use. I have discovered that selenium and/ or tellurium can be used in percentages ranging from 03% to 2.00% to improve the machinability of structural alloy steels with aminimum of non-metallic inclusions without inter- .fering with the ability of these steels to harden, and in many cases,'without substantial detriment to their use as finished parts.

I find that the machinability of structural alloy steels shows slight but noticeable improvement with percentages of selenium and/or tellurium as low as 05% and that the machinability increases progressively as the content of these metalloids is increased up to about .25%. Further additions up to 2% give further progressive improvement but at a slower rate so that I contemplate practically all free machining structural alloy steels can be satisfactorily made with between 05% and 25% selenium and/or tellurium. However it is to be understood that percentages between .25 and 2.00 achieve the purposes of my invention and are objectionable only because of the cost of the larger addition, the higher percentage of loss in making these large additions, and the general deterioration in the cleanness of the alloy by increasing the amount of non-metallic matter.

Quite small percentages of selenium and/or tellurium can also be used to supplement small as much as .07 to .08 which is sufficient to react favorably on the machining properties of the alloy. Thus my invention is commercially usable with selenium and/or tellurium even as low as 03%. 5

The use of phosphorus in structural alloy steels is as unpopular as the use of sulphur because of its embrittling efiects on the finished parts. However I have demonstrated that my selenium and/or tellurium addition, when su plemented by phosphorus yields even further improved machinability and this additional improvement is available in all cases where the embrittling effect of phosphorus does not interfere with the application of the alloy.

Phosphorus has a noticeable effect at 05% which increases progressively with further additions. Excessive brittleness is produced with phosphorus as high as 50% and I contemplate that commercially, the phosphorus will seldom be used in alloy steels in percentages-higher than about .12

Examples of the application of my invention to the three sub-groups of structural alloy steels herein before described are given below:

Carbon Molybdenuun.

Selenium .257 Tellurium 75 4,;

Free machining manganese steel l 50 38 48 "8 "8 1. ll F Silicon. 2. 62 .i .25 Phosphoru 015 000 .043 Sulphur .013 .016 .002 Chromium 1.00 Selenium .217 2.53 00 Machining tests made on the above examples confirm all of the other extensive experiments I have made in demonstrating the free machining effect of selenium and/ or tellurium permitting of faster cutting speeds with a cleaner finish on the machined articles. I observe in these free machining structural alloy steels the same antifriction and non-galling qualities that have been characteristic of the presence of selenium and tellurium throughout my experiments. It is wellknown to the art that the usefulness of many alloy steel parts such as pump shafts, bushings, bolts and nuts, slides, etc. depends to a considerable extent upon freedom of action in service or in assembly and disassembly. Any anti-friction or non-gelling qualities imparted to the alloy steel by the use of my invention contributes added value to the utilityof the parts.

Because of the poisonous nature of the fumes of tellurium emitted during the addition of this element to the molten steel bath I prefer to use selenium whenever possible. The exact quantitative equivalence of selenium and tellurium is not to be understood as I have frequently observed that tellurium is somewhat more potent for my purpose than selenium apart from other possible differences.

In the manufacture of my improved steel I have used elementalselenium and tellurium both in powder and stick form but I find it more desirable to first make an alloy of iron containing about 50% iron and 50% of the metalloid, and use this for additions to the molten bath. The 50% iron-metalloid alloy is heavy and is better assimilated by the bath with less loss by volatilization. In the manufacture of structural alloy steels in an electric induction furnace, the compounding of the base analysis proceeds as usual and a few minutes before pouring the heat of the ferro-selenium or ferro-tellurium are added and are quickly assimilated. The loss by volatilization may range from 10% for .10% metalloid addition with correspondingly higher losses for larger additions. In the electric arc furnace, the metalloid is best added to the flowing stream during tapping and the losses will be somewhat greater than in the induction furnace. In making open hearth alloy steels the metalloid is best added during the tapping operation but the losses may range 50% and higher due to the more oxidized condition of the metal. I regard tellurium as dangerous to use in the melting shop without proper protection for the workmen.

I have tested the machinability and noted the anti-friction qualities of structural alloy steels both in the cast and rolled condition and find that my invention applies equally well to castings and rolled, forged or drawn products.

In the sub-joined claims, the term balance substantially iron is used with the understanding that the ferrous balance may contain appreciable percentages of extraneous elements of such nature and'proportion that they do not alter the properties ofthe alloy for the purpose of my invention. For example, the presence of copper in a chrome-nickel steel would not alter the fact that it was in need of improved machinability and that the addition of my selenium and/ or tellurium elements provide such improvement. Hence such copper would be comprehended by my statement.

balance substantially iron.

What I claim is:--

1. The combination of .03% to 2% metalloidof the group selenium-tellurium with an inherently machinable structural alloy base; said base comprising 90% to 98% iron, carbon in an amount less than .50%, and the balance alloying elements, and being capable of annealing softer than 150,000 pounds per square inch ultimate tensile strength with more than 3% elongation in two inches; and the combination of said metalloidwith said base imparting materially improved machinability to the resulting alloy.

ferrous elements being between 2% and 9% and the balance being iron.

4. An alloy containing nickel 1% to 4.50%, chromium 25% to 1.75%, carbon in an amount less than .50%, metalloid of the group seleniumtellurium .05% to 50%, balance substantially iron with iron not exceeding 98%.

5. An alloy containing nickel 1% to 4.50%,

chromium .25% to 1.75%, carbon in an amount less than 50%, metalloid of the group seleniumtellurium .05% to 50%, phosphorus .05% to balance substantially iron with iron not exceeding 98%.

6. An alloy containing chromium to 4.00%, carbon in an amount less than 50%, metalloid of the group selenium-tellurium .03% to 2.00%, other alloying elements 25% to 5.00%, the total of nonferrous elements being between 2% and 9% and the balance being iron.

. 7. An alloy containing chromium 50% to 2.00%, carbon in an amount less than 50%, metalloid of the group selenium-tellurium .05 to .50%, alloys of the group molybdenum-vanadium .10% to 50%, balance substantially iron with iron not exceeding 98%.

8. An alloy containing chromium .50% to 2.00%, carbon in an amount less than 50%, metalloid of the group selenium-tellurium .05 to .50%, phosphorus .05% to 20%, alloys of the group molybdenum-vanadium .10% to .50% balance substan- 'tially iron with iron not exceeding 98%.

9. An alloy containing manganese .50% to 3.00%, carbon in an amount less than .50%, metalloid of the group selenium-tellurium .03% to 2.00%, other alloying elements 25% to 3.00%, balance iron with iron not exceeding 98%.

10. An v alloy containing manganese .50% to 2.00%, silicon 50% to 2.50%, carbon in an amount less than 50%, metalloid of the group selenium-tellurium .05% to .50%', balance substantially iron with iron not exceeding 98%.

'11. An alloy containing manganese .50% to 2.00% silicon .50% to 2.50%, carbon in an amount less than .50%, metalloid of the group seleniumtellurium .05% to .50%, phosphorus .05% to .20%,

balance substantially iron with iron not exceeding 98%.

FRANK R. PALMER. 

